Epoxy resins are used industrially in a wide variety of applications and their performance requirements are becoming increasingly more exacting in recent years. For example, resin compositions containing epoxy resins as main ingredients have been used typically as materials for encapsulating semiconductors and there is currently a demand for materials of improved solder heat resistance as an increase in the scale of integration of semiconductor devices has caused the packages to become larger in area and smaller in thickness and the packaging technology to shift to surface mounting. In consequence, there is a strong demand for encapsulating materials of reduced moisture absorption and improved adhesiveness at the interface of materials of different kind such as lead frames and chips. The same holds for materials for circuit boards and there is a demand for materials with properties of not only reduced moisture absorption, higher heat resistance and improved adhesiveness from the viewpoint of improving solder heat resistance but also reduced dielectric properties from the viewpoint of reducing dielectric loss. Moreover, in recent years, there is a trend toward elimination of halogen-based fire retardants from the viewpoint of reducing environmental load and this has created a demand for curing agents of improved fire retardance.
To meet these requirements, various novel structures have been investigated for epoxy resins which constitute the main ingredients on the side of epoxy resin suppliers and, concurrently, curing agents are receiving investigation.
As for base resins, there is a strong demand for improvements in moisture resistance, heat resistance and adhesiveness to metallic base materials.
However, none of the epoxy resins known thus far has satisfied the aforementioned requirements. For example, as is generally known, bisphenol type epoxy rest have found wide use as they are liquid at normal temperature, easy to work with and readily miscible with curing agents, additives and the like, but they face problems with resect to heat resistance and moisture resistance. Novolac type epoxy resins are known for their improved heat resistance, but they still have problems with respect to moisture resistance, adhesiveness and the like. Moreover, the conventional epoxy resins whose main skeleton is made up of hydrocarbons alone are completely devoid of fire retardance.
One of the measures known to improve fire retardance without the use of halogen-based fire retardants is to acid phosphate ester-based fire retardants. However, the addition of phosphate ester-based fire retardants fails to achieve sufficient moisture resistance. Furthermore, phosphate esters undergo hydrolysis in an environment of high temperature and moisture and lower the reliability of epoxy resins as insulating materials.
Studies are underway on the curing agents of epoxy resins. A candidate is naphthalene reins and an application of naphthol-aralkyl resins as encapsulants of semiconductors is disclosed in JP5-109934-A. Naphthol-aralkyl resins have excellent properties of low moisture absorption, low thermal expansion and the like, but show poor curability. Curing agents having a biphenyl structure are proposed in JP11-140166-A and described to be effective for improving fire retardance, but they are defective in curability. Moreover, since naphthalene-based resins and biphenyl-based resins have backbones made up of hydrocarbons alone, they were unable to manifest sufficient fire retardance.